78 Asa Arthur Schaeffer 



mine, the protozoan cannot express choice in food. The phrase 

 "selection of food" is evidently vague, and great care is necessary 

 in interpreting results when this concept is applied to specific 

 instances. In this paper the words "selection," "choice," etc., 

 are used only in a purely objective sense. 



These considerations, together with the fact that most protozoa 

 are observed to contain in their bodies only food materials in 

 various stages of digestion, has led the present writer to carry out 

 a number of experiments on this matter, using many substances, 

 digestible as well as indigestible. Because of large size, trans- 

 parency, sessile habit, and highly developed ciliary apparatus, the 

 Blue Stentor (Stentor caeruleus Ehr.) was selected as affording 

 probably the best opportunity for investigation. The question 

 proposed, was: Does Stentor ingest all particles that reach its 

 disk, or are swept into its pouch; or are some eaten and some 

 rejected, depending on whether they are or are not good for food.^ 

 This is the central question in this paper. A number of other 

 matters were also dealt with, as: the existence of conditions of 

 hunger and satiety; the basis of the selection, whether chemical or 

 tactual, etc. These questions will be taken up at their proper 

 places. 



MATERIAL 



The Stentors used in these experiments and the organisms used 

 for food were collected from a number of widely separated local- 

 ities, viz: Cold Spring Harbor, L. I.; Kunkletown, Pa., and various 

 places around Baltimore. This was done to determine whether 

 there were differences in Stentors that grew in different localities 

 with regard to the power of selecting food. After it was found 

 that Stentors from all localities and from laboratory cultures gave 

 practically the same results, the larger part of the work was done 

 upon specimens raised in the laboratory. All the organisms used 

 for food were also raised in the laboratory, excepting Phacus and 

 Euglena, which were always collected from wild cultures. The 

 food of the Stentors raised in the laboratory consisted of bacteria 

 and paramecia almost exclusively. Many of the Stentors which 

 were used in the experiments where Euglenae and Phacus were fed. 



